#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform float u_time;

float circle(in vec2 _st, in float _radius){
    vec2 l = _st-vec2(0.5);
    return 1.0 - smoothstep(_radius * 0.99, _radius * 1.01, dot(l, l) * 10.0);;
}

void main() {
    vec2 st = gl_FragCoord.xy/u_resolution;
    vec3 color = vec3(0.0);

    // 先给他放大五倍、在缩小在0-1之间
    st *= 5.0;
    st = fract(st);

    color = vec3(st, 0.0);
    // color = vec3(circle(st,0.5));

    gl_FragColor = vec4(color, 1.0);
}
